This invention relates to cleaning small parts, such as ink jet print head components, with a flow of gas from a nozzle.
In ink jet printing, ink is ejected from a narrow orifice in the direction of a substrate. In one type of ink jet printing, known as drop on demand printing, the ink is ejected in a series of droplets. The droplets may be produced and controlled using a piezoelectric ink jet head which has a large number of orifices, each of which is separately controllable to selectively eject ink at desired locations, or pixels, of the image. For example, an ink jet head may have 256 orifices that have a spacing for a printing resolution of 100 pixels (dots) per inch (dpi) or more. This dense array of orifices allows complex, highly accurate images to be produced. The quality of the images suffers, however, if one or more of the orifices becomes obstructed. For example, a partially obstructed orifice may alter the direction, size, or stability of the droplets. A drop on demand piezoelectric print head is described in U.S. Pat. No. 4,825,227, the entire contents of which is incorporated herein by reference.
In an aspect, the invention features an apparatus and method for cleaning with a flow of gas. In embodiments, a gas cleaning assembly is provided that includes a nozzle outlet that directs cleaning gas, e.g., toward a work piece, and a sheath gas jacket surrounding at least a portion of the nozzle that directs a sheath gas into contact with the nozzle. Embodiments may also include one or more of the following. The nozzle outlet and sheath gas jacket direct the sheath gas and cleaning gas generally toward a work piece. The sheath gas jacket and nozzle outlet direct the sheath gas and cleaning gas in generally opposite directions. The nozzle outlet and the sheath gas jacket direct the sheath gas both in a direction generally toward the work piece and generally away from the work piece. The flow of the sheath gas towards the work piece may be less than the flow away from the work piece. The sheath gas jacket is a generally tubular fitting having a first opening adapted to receive an exit end of the nozzle outlet and a second opening adapted to receive an inlet end of the nozzle outlet. The sheath gas jacket includes a sheath gas inlet for introducing sheath gas between the first opening and second opening.
In another aspect, the invention features a method using a gas cleaning nozzle by directing a cleaning gas through a nozzle and directing a sheath gas around the nozzle. The cleaning gas could be, for example, carbon dioxide. The sheath gas could be, for example either nitrogen or conditioned air.
Embodiments may have one or more of the following advantages. The sheath gas prevents condensation and ice buildup. A low flow of sheath gas surrounding the cleaning gas isolates the cleaning gas from humid environments while a high flow through the sheath gas jacket isolates the nozzle. The sheath gas jacket allows the user to clean a work piece without the problem of drops of water or particles of ice contaminating the work piece during a cleaning process. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.